The present invention relates to high voltage level shifting methods and circuits.
High voltage signal (up to several hundred volts) level shifting is an essential part of a modern power system. A high voltage signal level shifting scheme needs to provide isolation between the control signal and the switching power output. Conventionally, high voltage level shifting is realized through proprietary high voltage junction isolation technology, Hall Effect sensors or through optical isolation devices. All of these approaches disadvantageously have long propagation delays and low operating speeds. Emerging applications and system architectures, however, require high operation speeds, e.g. in the mega hertz range.
Furthermore, Hall Effect sensors or optical isolation devices are bulky, and not integratable on a chip. Moreover, conventional high voltage junction isolation (HVJI) technology is not compatible with standard low voltage CMOS technology and requires extra process steps, peripheral conditioning circuits, or multi step level shifting when signals are level shifted between two non-earth grounds.
In a conventional half bridge drive system, the DC bus is configured such that the negative DC bus voltage is at zero voltage. In a recent application, the DC bus is constructed as a split supply, which means the mid point of the DC bus is at zero voltage. In another recent application, the DC bus is configured as a floating split DC supply. For these two types of DC bus configurations, the conventional HVJI will require multi-step high voltage level shifting when input is at zero voltage, additional high voltage DC supply to hold the substrate to negative DC bus, additional input supply which is referenced to zero voltage.